On 11/27/2018 04:07 PM, Cong Wang wrote:

On Tue, Nov 27, 2018 at 3:48 PM Eric Dumazet [off-list ref] wrote:

quoted

But the padding might be added on normal packets (say 1000 bytes + 3 bytes of padding) ?

I never see other padding cases than ETH_ZLEN. Does ethernet standard
require padding for other cases? I only read the section "3.2.8 Pad field" in
the standard.

Padding can be done by senders, eg using AF_PACKET,
added at the tail of a regular IP/IP6 frame of 1000 or 6000 bytes.

Note that mlx5 will presumably set CHECKSUM_UNNECESSARY for standard protocols,
so if you want to reproduce the issue, you might need to find an IP frame that
mlx5 is not able to checksum validate.

Maybe a non-first fragment will do the trick.